Lifting apparatus for electric-line construction or maintenance workers



L. AsPLuNnH 3&1 08,656

4 Sheets-Sheet l Odi. -29, 1963 LIFTING APPARATUS FOR ELECTRIC-LINECONSTRUCTIQ 0R MAINTENANCE WORKERS Filed Aug..12, 1959 Y l ENToRATTQRNEYS '3,108,656 TRUCTION oct. 29', 1963 L. ASPLUNDH LIFTINGAPPARATUS FOR ELECTRIC-LINE CONS 0R MAINTENANCE -WORKERS 4 Sheets-Sheet2 Filed Aug. 12, 1959 ATTORNEYS Oct. 29, 1963 L. AsPLUNDH 3,108,556

LIFTING APPARATUS Foa ELEc'rRIc-LINE CONSTRUCTION OR MAINTENANCE WORKERSFiled Aug. 12, 1959 A 4 Sheets-Sheet 5;

ll ATTORNEYS v Oct. 29, 1963 L. AsPLuNDH 3,108,656

' LIETINC APPARATUS FCR ELECTRIC-LINE CONSTRUCTION 0R MAINTENANCEwoRKERs Filed Aug. 12, 1959 Y 4 Sheets-Sheet 4 v I ENT R Yfw ATTORN EY5United States Patent O 3 108,656 LIFTING APPARATUSFOR ELECTRIC-LINE CGN-STRUCTIGN GR MAINTENANCE WORKERS Lester Asplundh, Bryn Athyu, Pa.,assigner, by mesme assignments, to Asplundh Tree Expert Co., Jenkintown,

Pa., a corporation of Pennsylvania Filed Aug. 12, 1959, Ser. No. 833,34715 Claims. (Cl. 182-2) y'l'his invention relates to lifting apparatusand par-ticularly to equipment which is suitable for raising a workmanto a position where he has convenient access to electrical lines eitherfor the purpose of construction or maintenance of the line itself or fortrimmingthe branches of trees which may be interfering with the line. Asis well known workmen who perform these duties are often subjected todanger especially when servicing lines which carry high voltages orheavy current loads. Beyond this, the truck or base upon which thelifting equipment is mounted is often a potential danger to those whomay be working on or around it on the ground because a short circuitthrough the equipment may seriously injure or even kill a man whotouches the appartus while in contact with the ground. To use anexpression which is [familiar to the industry a truck which is carryinga short circuit to the ground is known as a hot truck.

The primary object of the present invention is to construct equipment orapparatus of the character described which will completely protecteither the workman who is elevated above the ground or a man on or incircuit with the ground from all danger due to shorting of chargedwires. At the same time it is an object of my invention to provide forsuch safety in equipment of this kind without in any way interferingwith its mobility or maneuverability.

It is also an object of my invention to provide means whereby theworkman who is supported above the ground can maneuver himself intowhatever position is most convenient for the work in hand and also bymeans of which someone standing on the ground or located in the truckcan also maneuver the workmans platform to whatever position may bedesired, and both of these without danger of injury from short circuitsor structural deliciencies.

-A still further object is to provide the required insulation throughuse of structural, load-carrying members or parts which are constructedof electrically non-conducting material as distinguished from the use ofstructural parts which in themselves are not non-conducting and are onlysurfaced or covered with insulating material. The latter type ofequipment is known in the art and has many times proved to beunsatisfactory because it is relatively easy to so seriously damage theinsulating covering as to endanger the workmen. Such dangerousconditions can be developed under normal service conditions or throughcareless handling of the equipment and may result from scraping, bumpingor breaking -the insulating surfaces, and this without knowledge ofthose involved and often without discovery even upon careful inspection.

Still another object of the invention is to provide suitable raising andlowering equipment as well as platform leveling equipment which is alsothoroughly insulated in order to prevent short circuiting from the wiresto the ground.

How the foregoing objects together with such other objects as may appearhereinafter or are incident to my invention are attained is illustratedin preferred form in the accompanying drawings wherein FIGURE 1 is asomewhat diagrammatic elevational view of my improved lifting apparatusmounted upon a 3,108,656 Patented Oct. 29, 1963 p ICC truck with aportion of the upper boom used in the apparatus broken out to show `theplatform leveling cables with their insulating means;

FIGURE 2 is an enlarged plan section taken on the line 2 2 of FIGURE Il;

FIGURE 3 is an enlarged fragmentary section taken as indicated by theline 3 3 of FIGURE 4;

FIGURE 4 is a vertical section through the supporting mast or pylon andthrough the lower portion of the lower boom which is pivotally mountedthereon;

FIGURE 5 is a plan section on the line 5 5 of FIG- URE 4;

FIGURE 6 is a sectional elevation of portions of the lower and upperbooms including the point where they are articulated together;

FIGURE 7 is an exploded view of the mast or pylon structure;

FIGURE 8 is a view taken on the line 8 8 of FIG- URE 9 showing the upperboom and the workmans platform or basket which is pivoted at the outerend thereof;

FIGURE 9 is a plan section on the line 9 9 of FIG- URE 8;

FIGURE 10 is an enlarged fragmentary sectional elevational view of thelower portion of the mast or pylon and the so-called pylon box;

FIGURE 1l is an enlarged fragmentary section on the line Il l of FIGURE8; and

FIGURE 12 is a section on the line 12 12 of FIG- URE 6.

`By referring to the drawings, it will be seen that I have mounted myimproved lifting apparatus upon a truck T so as to provide for a highdegree of mobility. Preferably the mounting point is on the chassis 13directly in back of the cab 14 because this is a location which providesfor the highest degree of stability. A mast or pylon box 15 is arrangedat the back of the cab as shown in FIGURE l, which box is constructed toprovide suitable bearing means for the vertical mast or pylon 16 as willappear below. It also houses the horizontally disposed hydrauliccylinder and piston mechanism 17 18 which rotates the mast together withcertain of the hydraulic valve controlling mechanisms and fluid lines.An outrigger 19 is provided at each side of the pylon box which isadapted to engage the ground to ensure stability when the appartus is inuse. These outriggers, however, form no part of the present invention.

With my invention I prefer to construct the vertical mast or pylon I6 ofthree principal parts, namely a stuk mast or section 2d at the bottom,an upper mast portior or section 2l and an intermediate load-carryingmas member or section 22 which latter is constructed entirely of asuitable electrically non-conductive material of suffi cient structuralstrength to carry the loads and resist tht stresses incident tooperation of the lifting apparatus. Thi: intermediate section is mountedon the stub mast to ro tate therewith and project upwardly therefrom andtht upper mast section is mounted on the intermediate sec tion also torotate therewith, so that the whole mas structure constitutes arotatable pylon for supporting tht booms to be described below.

Preferably the sections 20, 2l and 22 of the'mast o pylon are tubular inform with their adjacent ends ar ranged to telescope. I provide for thistelescoping bj making the stub section and the upper section of slightljlarger diameter than the adjacent end portions of the in termediateinsulating section so that they will embrace th adjacent ends of theintermediate section as indicated it` best advantage in FIGURES 1 `and7. Furthermore, th

intermediate non-conducting section 22 is provided wit an annularshoulder 23 of substantial extent longitudina ly of the section, againstthe vupper face of which shou der the bottom end of section 21 abuts andagainst the under face of which shoulder the upper end of the stubsection 20 abuts when the parts are in assembled relation. rIihe stubsection 20 and the upper section 21 are preferably composed of suitablemetal but it will be obvious that no electrical path from the uppersection 21 to the lower section 20 exists because the intermediatesection 22 with its shoulder .-23 prevents contact of the upper sectionwith the lower section. Furthermore, the width of the shoulder 23 isdesigned to resist jumping of current from the upper section to thelower section up to voltages as high as will be encountered in theservice for which the lifting apparatus is intended. In some instances`this may be as much as 100,000 volts,

My preference, insofar as material from which to construct theinsulating section 22 is concerned, is Fibreglas in which the fibres arespun to the shape :desired and bonded `with suitable bonding material,because I have found that a unit constructed in this way is fullynon-conductive and of outstanding strength from a structural standpoint.At the same time it can be made within very practical and reasonablelimits insofar as size is concerned.

The three sections of the mast are fitted and secured together so thatthey rotate as a unit, the bottom section 20 being mounted on thehorizontal wall 24 near the bottom of the pylon box in a suitablebearing 25. The upper end of the section 20' passes through the upperwall 26 of the pylon box `where it is provided with another bearing 27.

Ata point between the bearings 25 and 27 and preferably near the upperbearing 27 as shown in FIGURE 10, the stub section 20 of the mast isprovided with a pulley surface 2S and adjacent thereto is the horizontalhydraulic cylinder 17 with its piston 1S already referred to. The pistonis double acting and projects from both ends of the cylinder and on eachend of the piston is a pulley 29.

A cable 30 `for rotating the mast leads from the upper bracket 31 on thecylinder 17 to the lower pulley 29 (las viewed in FIGURE then to thepulley surface 2S which is secured to the section 20' and around thispulley 2S one turn and finally up to and around the upper pulley 29 andthen down to the lower bracket 32 on the cylinder 17 (still viewed as inFIGURE 5). This cable 30 is secured at a central anchor 33 on the pulley28.

High pressure hydraulic operating fluid comes in through the supply pipe34 (FIGURE l0) .which delivers it to the valve housing 35 in which islocated a series of control valves the details of which are notillustrated because, per se, they `form no part of the presentinvention. Suflice it to say at this point that an upper valve chamber36 controls the fluid which operates the piston 1S in the cylinder 17,the -iiuid circulating and returning through the lines 37. A lever 33 isprovided in the pylon box within easy reach of a workman on the groundby means of which, if desired, he can cause rotation of the mast.

The Khandle 38 for actuating the valve which controls the operation ofthe cylinder and piston I7-18 can also be operated by the workman up onthe platform or basket 66. To this end a valve actuating cylinder andpiston mechanism 39 is provided -which is under the control of the lowpressure hydraulic lines 40 leading up to a low pressure valve controlmechanism in the basket within convenient reach of the workman `as willfurther appear.

A lower boom 41 is suitably pivoted for up and down swinging movement ina forked member 42 secured to the top of the upper mast section 21 (seeFIGURES 1 and 3). Swinging motion of the boom `411. takes place aroundan axis shaft 43 which, for convenience, will be referred to as lthepylon shaft. This pylon shaft is fixed against rotation in the forkedmember 42 and the boom 41 swings thereon through the medium of suitablebearing construction shown in FIGURE 3 but 4which will not be describedin detail since in and of itself it forms no part of the pres- :ntinvention. For a purpose which will appear hereinafter, the shaft 43also carries a sheave 44 which is fixed to the shaft 43. The sheave 44,therefore, never rotates at all because it is fixed on the shaft 43y andthe shaft 43 is fixed in the forked member 42 as described.

Still referring to FIGURE 3 it will be seen that a boom operating sheave45 is `also mounted on the shaft 43 Iwhich sheave is free to rotate onthe shaft. The cable 46 which raises and lowers the upper boom 47 passesaround this sheave 45 as will further appear.

The lower boom 41 is raised and lowered around its pivot on shaft 43 bymeans of a hydraulic cyl-inder and piston mechanism 48-49, the lower endof the cylinder 48 being suitably pivoted on the upper section 21 of themast and the outer end of the piston 49 being suitably pivoted to theboom 41 at a point just above the shaft 43. By so placing the cylinderand piston 48-49 it cannot act as a short circuit to the ground becauseits points of connection are above Ithe insulating mid section 22--23 ofthe mast or pylon. The high pressure hydraulic fluid for actuating thecylinder land piston mechanism 48-49 and so raising and lowering thelower boom 41 is delivered and returned through lthe h-igh pressurehydraulic lines 50 under the control of a suitable valve in the box 51(see FIGURE 10). An actuating lever 51a is provided for moving the valvein box 51 and, as in the case of lever 38, it may be actuated by aworkman on the ground as well as by the workman up in the basket throughthe medium of low pressure fluid lines 51b and an operating cylinder51e.

The upper boom 47 is pivoted on the upper end of the lower boom 4I bymeans of the following construction (see particularly FIGURES 1, 2, 6and 12). At its lower :end the upper boom 47 is provided with an endmember 52 which is bolted to an extended hub portion 53 of an `operatingsheave 54 (see FIGURE 2). The sheave 54 with its extended hub 53 rotatesin bearings in a fixture 56 which latter is attached to the upper end ofthe lower boom 41. In turn the sheave 54 supports, in suitable bearings,a hollow shaft 55 which latter extends from a point within the upperboom end member 52 outwardly through sheave 54 to the inside of theupper end of the lower boom 41. The bearings for the shaft 55 are shownto best advantage in FIGURE 2. On the end of .the shaft 55 within ythemember 52 there is fixed a leveling pulley 57 and. at the opposite endof the shaft 55 there is fixed another leveling pulley 58. Both of theseleveling pulleys therefore can turn with the shaft 55 during levelinglof the basket as will further appear.

In order to swing the upper hoorn 47 upwardly and downwardly a highpressure, fiuid-actuated cylinder and piston mechanism 59-60 isprovided, the cylinder being mounted on the lower boom 41 as shown inFIGURES l and 6. The sheave 54 is a double sheave `as shown in FIGURE 2and the operating cables are `anchored to this sheave at the points 62and 63 (see FIGURE 6). The anchor 63 is the anchor for the right handrun 46a of the cable which run is in the sheave groove closest to theobserver in FIGURE 6. In other words, the right hand cable run in FIGURE6 leads upwardly from the piston rod 60 into and around the front groovein the sheave 54, then over the sheave for approximately 3A of a turn tothe anchor 63 near the bottom of the sheave as viewed in FIGURE 6. Theleft hand run 4611 of the cable leads from the connection 61 at thebottom of the cylinder 59 to and around the lower sheave 45 and then upyto `the other groove of the upper double sheave 54 (as viewed in FIGURE6) and then approximately I/a turn to the right `around the said sheave54 to the anchor 62. Therefore, when the hydraulic operating fiuid iscirculated to and from the cylinder 59 the cable runs 46a and 46b willrotate the sheave 54, the hub S3 of which is connected to the lower endof the upper boom 47 so that said upper boom may be swung upwardly anddownwardly in its bearings in x-ture 56. Here again the mechanism justdescribed, namely 4the cylinder and piston mechanism 59-60 with thecable 46 cannot create a short circuit to the ground because of the factthat they are located entirely above the insulating section 22.-23 ofthe pylon.

High pressure iluid for operating the cylinder and piston mechanism59-60 is delivered through the conduits 64 under the control of thevalve in box 65 (FIGURE lever 65a and low pressure actuating cylinder65C and low pressure lines 65b which latter lines as before run up tothe operating platform or basket at the top of the upper boom.

At this point I wish to call particular attention to the fact that thehydraulic flu-id lines 40, Slb, 50, 64 and 65h are made entirely ofsuitable electrically non-conductive material such as nylon or rubber sothat none of them can possibly act as conductors for carrying `a shortcircuit from the electric line above to the ground below. The hydraulicfluid lines 37 need not be made of nonconductive material because theyextend only to -tlhe cylinder and piston mechanism 17-18 and are locatedwithin the pylon box at a point below the insulating section 22-23.

The platform which takes the form of a suitable basket 66 is pivoted onthe outer end of the upper boom in the following manner (seeparticularly FIGURES 8, 9 and l1). At 'one side near the top, a shaft 67is welded or otherwise securely fastened to `the basket so that theshaft and the basket move together. This shaft 67 projects outwardlythrough the upper end tting 68 of the upper boom 47 and is mounted insuitable bearings 69. Fastened to the shaft 67 is a leveling pulley 7d.As the booms are raised and lowered the basket also must be swung eitherto the right or to the left in order to maintain it substantially levelat all times. This is accomplished by means of the leveling sheaves 44,57, 58 and 70 already referred to and the leveling cables 71, 72, 73 and74 which are reeved thereon. Each of cables 71 and 72 is secured by asuitable `anchoring means 75 on the upper portion of the sheave 44 (seeFIGURE 3). 'Ilhe llower end of each cable 71 and 72, therefore, passesroughly three quarters of `a turn 'around the leveling pulley 44.Similarly, on the sheave 5S at the upper end of the lower boom the endsof the leveling cables 71 and 72 are passed approximately three quartersof a turn around the sheave rand then anchored at a point in the lowerportion of the sheave. A similar arrangement exists for the levelingcables 73 and 74, their low-er ends being passed three quarters of aturn around the sheave 57 in opposite directions and then anchored tothe sheave. Finally, the basket ends of the leveling cables 73 and 74pass around the basket sheave 70v to a suitable anchor 7 6 near thebottom of this sheave.

Since the bottom leveling sheave or pulley 44 is firmly xed and neverrotates at all it is obvious that when the lower boom swings upwardly ordownwardly on its pivot the leveling cables 71 and 72 will be wrappedaround or unwrapped from the leveling pulley 44. For example, when thelower boom 41 swings downwardly toward the right on its pivot from theposition shown in FIGURE 1 the left hand leveling cable 71 will bewrapped on the fixed pulley 44 to effect counterolockwise rotation ofthe sheave 58, shaft 55 and sheave 57. This causes the cable 74 torotate the basket sheave 7@ in a counterclockwise direction so as toswing the basket to the right and thereby maintain it in level positionas the lower boom is swung downwardly. It is obvious, of course, thatthe reverse action takes place when the lower boom is swung upwardlyback to the position of FIGURE 1 and also when it is swung downwardlytoward the left from the position of FIGURE l, i.e., the sheave 5S,shaft 55, sheave 57 and sheave 70 are rotated in a clockwise directionso as to swing the basket to the left and thereby again maintain it inlevel position. An entirely analogous or similar action takes place whenthe upper boom is swung on the lowerV 6 boom because at such times theleveling pulleys in the joint which connects the two booms will be heldin iixed position by the leveling cables in the lower boom. Of course,it will be obvious that a composite result of such motions will beeffected where both booms are being swung simultaneously.

I now wish to refer to other important insulating features of myimproved apparatus. The upper boom 47 has the major portion of its shankconstructed completely of some suitable, structural, electricallynon-conducting material such as Fiberglas spun and bonded together. Asin the case lof the pylon section 22f-23 I prefer Fiberglas for thispurpose because of its absolute insulating qualities and its greatstructural strength. Indeed, I have determined by extensive tests that aboom constructed in this way will resist, for very long periods, alldestructive effects of the forces created during operation of theapparatus.

It will be seen, therefore, that, insofar as the upper boom isconcerned, I have in the present disclosure, shown it as involving apair of spaced end members or ttings which are interconnected by a longtubular section or shank of spun glass fibres bonded together into arigid, load-carrying structural member lthrough which it is absolutelyimpossible for any current to pass in case the upper end of the boomstructure or the basket itself should come into contact with a livewire. The workman in the basket, therefore, is completely protectedagainst any possible injury unless he should himself :grasp two hightension lines, one with each hand.

I should also like to point to certain features of construction whichare important. One of these is involved in the fact that the booms andthe mas-t are all of hollow tubular construction and that `the levelingcables are completely housed therein. This in itself is a greatprotection insofar as short circruiting is concerned, but in addition Iprovide long sections 73a and 74a for the upper leveling cables 73 and74 which sections are constructed of suitable, electricallynon-conducting material such as nylon so that in the event of damage toany portion of the upper boom or its associated structure it would` notbe possible for current to pass down through the leveling cables to thelower portions of the apparatus.

I also wish to mention certain details with respect to the means wherebythe operator in the basket 66 can maneuver himself into the bestpossible position for the work he is doing. At the side of the basketwithin easy reach of the operator are a plurality of levers (in thiscase three levers) 76, 77 and 78, which levers control valves for thelow pressure hydraulic system, the fluid for which passes upwardly anddownwardly through the low pressure lines 4t), 51b and 65:5 alreadydescribed. By manipulating the handles 76, 77 and 73 the operator canmove the valve levers 38, 51a and 65a which, respectively, causerotation of the mast, raising and lowering of the lower boom or raisingand lowering the upper boom. Furthermore, all of the low pressurehydraulic lines just mentioned are arranged together in a bundle 82 andpassed along the inside of the booms and the mast so `that they are atall times well housed and well protected against damage. At the basketthis bundle of low pressure hydraulic tubes i: coupled in the forim of atlexible coil preferably of rubber material 79 which surrounds the shaft67, one end of the coil being secured to the basket at 8G and the otheren( to the boom, At the joint between the booms this bundlf of lowpressure hydraulic tubes passes through the hollov center of the pivotshaft 55 and then into the shield mem ber 81 and from thence into the.interior of the lowei boom. At the bottom of the lower boom it passesarounc the hub of the sheave 45 as indicated at 82a in FIGURE 4. Afterpassing the sheave hub 45 the bundle passe down through the interior ofthe mast or pylon and out a the bottom in the lower space 15a of theplyon box ani then upwardly to the valve operating cylinders and pistonas shown in FIGURE l0.

Since the improvements described eliminate all possibli arcanes ,a7pathways or conductors along which current might iiow from the wires tothe ground it will be seen that 'workmen either in the rbasket or on theground are fully protected against injury. Furthermore, the :basket canbe maneuvered to proper position either by a rnan in the basket or by alman on the truck or on the ground and `the several motion producingdevices by which the position of the backet is adjusted are controlledfrom the basket by controlling connections which are inherentlynon-conducting. In other words by the present invention all wires orother possible electrical pathways between the lines and the ground areeliminated.

I claim:

l. A structure for supporting a lifting boom or the like, comprising abase, a stub mast rotatably mounted on the base, a load-carrying mastmember constructed entirely of electrically non-conductive materialmounted on the stub mast to rotate therewith and project upwardlytherefrom, and an upper mast section mounted on the non-conductive mastmember to rotate therewith, the lifting boom being pivoted on said uppermast section.

2. Apparatus according to claim l wherein the load carrying,electrically non-conductive mast member is formed of glass fibers bondedinto the form of a tube and wherein a hydraulic cylinder and pistondevice for raising and lowering the boom is provided, said devicereacting between the boom and the upper mast section, and still furtherwherein electrically non-conductive tubing is provided for carrying thehydraulic uid to and from the cylinder.

3. In apparatus for elevating a man and supporting him from a positionon the ground in an elevated location for work on and aroundelectrically charged overhead wires, said apparatus comprising a truck,boom supporting means on the truck, said boom supporting means beingrotatable in a horizontal plane, a boom articulated to said supportingmeans for vertical swinging movement, and a workmans platformarticulated to the boom and supported for vertical swinging movementupon a horizontal pivot; the combination therewith of the improvementfor reducing the workmansl hazards which includes an extended length ofboom being constructed entirely of dielectric material formed as ahollow structural member adapted to carry the platform load and resistthe stresses developed during use of the apparatus.

4. An apparatus according to claim 3 wherein said boom supporting meansincludes an upright mast of which an extended section is alsoconstructed entirely of dielectric material adapted to carry the boomand its load and resist the stresses developed during use of theapparatus.

5. An apparatus according to claim 3 wherein the dielectric material inthe boom consists of glass fibers bonded together to form the hollowstructural member.

6. Lifting apparatus comprising a base, a tubular pylon rotatablymounted on the base, said pylon including a tubular load-carrying mastmember constructed of electrically non-conductive material, a tubular`first or lower boom pivoted for up and down swinging movement on saidelectrically non-conductive mast member, a tubular second or upper boompivoted for up and down swinging movement on the outer end of said lowerboom, said upper boom having the major portion of its length formed of aload-carrying, electrically non-conductive material, a workmans platformpivoted on the outer end of said upper boom, and leveling cable for .theplatform extending through the interior of said tubular booms, saidcable where it traverses the interior of the upper boom including amajor length of electrically non-conducting material.

7. In apparatus for elevating a man and supporting him from a positionon the ground in an elevated location for work on and aroundelectrically charged overhead wires, said apparatus comprising a truck,an upright mast mounted on the truck, a boom mounted for verticalpivoting upon said mast, a workmans platform articulated to the boom andsupported for vertical swinging movement upon a horizontal pivot, ahydraulic cylinder and piston device for raising and lowering the boomand uid pressure supply conduits for the cylinder and piston device; thecombination therewith of the improvements for reducing the workmanshazards which include the upright mast being constructed with a lowerstub section rotatably mounted on the truck, an upper section upon whichthe boom is pivoted and an intermediate section formed entirely ofelectrical insulating material of suflicient strength to carry the boomand its load and resist the stresses developed during use of theapparatus, the hydraulic cylinder and piston device being arranged toreact between the boom and said upper mast section and said fluidpressure supply conduits being formed of electric insulating material.

8. In apparatus for elevating a man and supporting him from a positionon the ground in an elevated location for work on and aroundelectrically charged overhead wires, said apparatus comprising a truck,an upright mast mounted on the truck, a boom mounted for verticalpivoting upon said mast, and a workmans platform articulated to the boomand supported for vertical swinging movement upon a horizontal pivot;the combination therewith of the improvements for reducing the workmanshazards which include an extended length of the boom being constructedentirely of dielectric material of sulicient strength to carry theplatform load and resist the stresses developed during use of theapparatus, and with the upright mast being constructed with a lower stubmast section rotatably mounted on the truck, an upper mast section uponwhich the boom is pivoted and an intermediate mast section formedentirely of electrical insulating material of sucient strength to carrythe boom and its load and resist the stresses developed during use ofthe apparatus, said intermediate and said upper mast sections rotatingwith said lower stub section to provide for horizontal rotation of theboom around the axis of the mast.

9. In apparatus for elevating a man and supporting him from a positionon the ground in an elevated location for work around electricallycharged overhead Wires, said apparatus comprising a truck, hollow upperand lower booms pivotally interconnected, a vertical mast structureincluding a rotatable mounting carried by the truck by means of whichsaid booms may be supported and moved in a horizontal plane, a Workmansplatform swingably secured to the outer end of the upper boom upon ahorizontal pivot, platform leveling cable housed in the booms, iiuidpressure motor means for adjusting the inclination of each boom andfluid pressure supply conduits for said motor means; the combinationtherewith of the upper boom having an extended section thereof formedentirely of electric insulating material consisting of glass iibersbonded together to form a structural member of sufhcient strength tocarry the platform load, together with a supporting insert in saidvertical mast constructed entirely of electric insulating material ofsuiiicient structural strength to carry the booms and their load, saidleveling cable in the upper boom including extended sections consistingentirely of electric insulating material and said uid pressure supplyconduits being formed entirely of electric insulating material.

l0. In apparatus for elevating a man and supporting him from a positionon the ground in an elevated location for work on and aroundelectrically charged overhead wires, said apparatus comprising a truck,a hollow upright mast carried by the truck, a hollow boom mounted forvertical pivoting upon said mast, a workmans platform swingably securedto the outer end of the boom upon a horizontal pivot, platform levelingcable housed in the booma fluid pressure actuated motor means foradjusting the inclination of the boom, and iluid pressure supplyconduits housed in the mast; the combination therewith of theimprovements for reducing the workmans hazards, which include anextended portion of the length of the boom being constructed entirely ofelectric insulating material of suiiicient structural strength to carrythe platform load, an extended portion of the length of said mast alsobeing constructed entirely of electric insulating material of suicientstructural strength to carry the boom and its load, an extended sectionof said leveling cable also being formed entirely of electric insulatingmaterial, and, still further, said iluid pressure supply conduits beingformed of electric insulating material.

11. In apparatus for elevating a man and supporting him from a positionon the ground in an elevated location for work on and aroundelectrically charged overhead wires, said apparatus comprising a truck,boom supporting means on the truck, said boom supporting means includinga horizontally rotatable mounting on the truck and a mast-like,boom-supporting member projecting from said rotatable support, a boompivoted on said mast-like member for vertical swinging movement, and aworkmans platform articulated to the boom and supported for verticalswinging movement upon a horizontal pivot; the combination therewith ofthe improvements for reducing the Workmans hazards which include anextended section of boom being constructed entirely of electricinsulating material of suiiicient structural strength to carry theplatform load and an extended section of said mast-like member beingconstructed entirely of electric insulating material of suiiicientstructural strength to carry the boom and its load.

12. An apparatus according to claim 11 wherein said electric insulatingsections consist of glass fibers bonded together in the form of hollowstructural members.

13. An apparatus according to claim 11 wherein the boom is hollow andwherein platform leveling cable runs between and is reeved around saidpivots and is housed in the boom with each run of the leveling cableincluding an extended section formed entirely of electric insulatingmaterial.

14. ln apparatus for elevating a man and supporting him from a positionon the ground in an elevated location for work on and aroundelectrically charged overhead wires, said apparatus comprising a truck,boom supporting means on the truck, said boom supporting means beingrotatable in a horizontal plane, upper and lower booms pivotallyinterconnected and with the lower end of the lower boom being pivoted onsaid supporting means for vertical swinging movement, and a workmansplatform supported for vertical swinging movement upon a horizontalpivot at the outer end of the upper boom; the combination therewith ofthe improvement for reducing the workmans hazards which includes anextended length of boom being constructed entirely of dielectricmaterial adapted to carry the platform load and resist the stressesdeveloped during use of the apparatus.

15. An apparatus according to claim 14 wherein said boom supportingmeans on the truck includes an upright mast to which the boom isarticulated and further wherein an extended section of said mast isconstructed entirely of electrical insulating material of suicientstructural strength to carry the boom and its load.

References Cited in the le of this patent UNITED STATES PATENTS 433,001Hall July 29, 1890 1,786,631 Roe Dec. 30, 1930 2,091,852 Hinds Aug. 31,1937 2,616,768 Stemm Nov. 4, 1952 2,666,417 Harsch Jan. 19, 19542,798,623 Girardi July 9, 1957 2,825,752 Kuntz Mar. 4, 1958 2,881,030Troche Apr. 7, 1959 2,915,137 Troche Dec. 1, 1959 2,936,848 Hall May 17,1960 2,940,539 Richey lune 14, 1960 OTHER REFERENCES Aerial Platform,from the publication Electrical World, vol. 151, No. 26, page 133.

3. IN APPARATUS FOR ELEVATING A MAN AND SUPPORTING HIM FROM A POSITION ON THE GROUND IN AN ELEVATED LOCATION FOR WORK ON AND AROUND ELECTRICALLY CHARGED OVERHEAD WIRES, SAID APPARATUS COMPRISING A TRUCK, BOOM SUPPORTING MEANS ON THE TRUCK, SAID BOOM SUPPORTING MEANS BEING ROTATABLE IN A HORIZONTAL PLANE, A BOOM ARTICULATED TO SAID SUPPORTING MEANS FOR VERTICAL SWINGING MOVEMENT, AND A WORKMAN''S PLATFORM ARTICULATED TO THE BOOM AND SUPPORTED FOR VERTICAL SWINGING MOVEMENT UPON A HORIZONTAL PIVOT; THE COMBINATION THEREWITH OF THE IMPROVEMENT FOR REDUCING THE WORKMAN''S HAZARDS WHICH INCLUDES AN EXTENDED LENGTH OF BOOM BEING CONSTRUCTED ENTIRELY OF DIELECTRIC MATERIAL FORMED AS A HOLLOW STRUCTURAL MEMBER ADAPTED TO CARRY THE PLATFORM LOAD AND RESIST THE STRESSES DEVELOPED DURING USE OF THE APPARATUS. 